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ContentProvider that sends form data


This provider creates data suitable for a request message whose Content-Type is "application/x-www-form-urlencoded", as required by many servers that expect users to fill in HTML forms.

Using this provider in the Body of a RequestMessage is optional, because you can insert a QueryParameter vector directly into the Body of a RequestMessage to get the same conversion done automatically.

Subclass authors can create a FormProvider subclass to create the data dynamically only when the message is ready to be transmitted, or during transmission.


provider = FormProvider(queryparams) constructs a provider that sends a vector of QueryParameter objects specified as queryparams. This constructor sets the Parameters property to the value of queryparams.

provider = FormProvider(arg1,...,argn) sends an arbitrary list of arguments to the constructor to obtain a QueryParameter vector. This syntax a shortcut for:


Input Arguments

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One or more input arguments to the constructor, specified as valid argument types. If your arguments are already encoded, append a 'literal' argument to the end of the list.


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Query parameters, specified as a vector or cell array of objects as passed into or derived from the arguments to the constructor. To see the body of the message, use the string method.



Set by MATLAB or Delegator

Request message to send, specified as a object.

This property is used only by subclass authors. The RequestMessage.send and RequestMessage.complete methods set this property to the RequestMessage in whose Body this provider has been placed, before calling any other methods in this provider, and before adding any additional header fields or validating the message. The provider can examine this message to see what was contained in the original request.

Delegates see the same value for this property as the delegator. ContentProviders should be aware that, if they are delegates, they are not necessarily providing the entire body of the request message, so they should not assume that header fields in this Request are pertinent to the data they are providing. Usually, delegates should ignore header fields in this request relevant to the data, such as Content-Type.

If the provider wishes to add any header fields to this message, or to modify existing ones, it should do so in its complete method by adding those fields to the Header property. The caller of complete (RequestMessage or a delegating provider) determines what to do with those fields. RequestMessage.send and RequestMessage.complete always copy these fields to the Header of the RequestMessage. A delegating provider can copy the fields to its own Header property or insert them into the message (as in the case of MultipartProvider). For more information, see the Header property.

This property is read-only.



ContentProvider that delegated to this provider, specified as a object.

If a ContentProvider delegates responsibility for sending all or a portion of the message data to another provider, then this property identifies the delegating provider to the delegate. For example, a MultipartProvider delegates parts of the message to other providers, so it inserts a handle to itself in each delegate. Otherwise, MyDelegator is empty. The delegateTo method sets this property in the delegate.



Set by Provider or MATLAB, Read by MATLAB

Header fields of the message or part, specified as a vector of one or more objects.

This property is only used by subclass authors. MATLAB® sets this property before calling the provider's complete method. For non-multipart messages, MATLAB initializes this property to the contents of Request.Header, minus any or empty-valued fields. The ContentProvider uses this property to add header fields that describe the data to be sent, or to add parameters to header fields already in the message. In a delegate for a MultipartProvider, MATLAB initializes this property to header fields that the delegating provider intends to insert for the part. Delegates can modify or change these fields.

Upon return from the provider's complete method, if this not a multipart message, then MATLAB reads this property and merges its contents into the header of Request. Fields in this Header with Names that do not already appear in Request.Header are added to the end of Request.Header. If a field in this Header has a Name that is the same as one in Request.Header, and both have nonempty Values, then:

  • If the one in Request.Header is a GenericField, then ignore the one in Header.

  • If the one in Request.Header is not a GenericField, then replace it with the one in Header.

If one or both of these has an empty Value, then the field is removed from Request.Header and it is not added as part of normal message completion.

If this is a delegate of a MultipartProvider, then the entire contents of this Header is used as the header of the part. Multipart delegates must not assume that Request.Header contains any fields pertaining to their own Header. A provider can determine whether it is a multipart delegate by checking whether MyDelegator is a MultipartProvider, though this test is unlikely to be needed.

MATLAB reads this property only on return from calling the provider's complete method. Changes to this array are ignored once MATLAB calls start.

Class authors should be aware that their subclasses might have added fields to this Header (in their complete method) before calling complete in their superclass. It is best to preserve such fields and not to add fields with the same names. However, adding a parameter to a field is permissible. For example, a superclass can add a charset parameter to an existing Content-Type field that does not already have one.



Indicate whether to force chunked transfer coding, specified as boolean. This property is of interest only to subclass authors, and is applicable only to providers that are not multipart delegates. Subclasses set ForceChunked to control whether contents should be sent using chunked transfer coding. If false (default), MATLAB decides whether to send the contents chunked, based on whether it knows the content length at the time the message is ready to be sent:

  • If MATLAB knows the content length (which is the case if the message contains a Content-Length field, or if this provider's expectedContentLength method returned a number), then MATLAB decides whether to send it chunked or not.

  • If MATLAB does not know the content length (no Content-Length field in the header and expectedContentLength returned empty), then MATLAB always sends the message chunked.

If ForceChunked is true, then MATLAB sends the message chunked regardless of whether it knows the content length, unless the known length is smaller than the chunk size. If this property is true, then the message must not contain a Content-Length field, because HTTP does not allow a chunked message to have a Content-Length field. However, you can still return a nonzero value in the expectedContentLength method if you want MATLAB to verify that you are returning the expected length of data.

When MATLAB chooses to send the message chunked, the size of each chunk is equal to the length of data returned by getData.

MATLAB reads this value after calling the complete method, before calling start. It does not set this field.



ContentProvider to which this provider is delegating, specified as a object. This property is set in the calling provider (the delegator) by the delegateTo method to indicate the current delegated provider. If there is no current delegation, then the value is empty.

The complete methods set this property to empty.



stringFormProvider Data property

Inherited Methods

completeComplete HTTP header for StringProvider
getDataNext buffer of data to send in HTTP request message from StringProvider
startStart data transfer from StringProvider
stringStringProvider Data property

Class Hierarchy

Introduced in R2018a